• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.255-268
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• 2018

Subsea tunnel can be highly vulnerable to seawater intrusion due to unexpected high-water pressure during construction. An artificial ground freezing (AGF) will be a promising alternative to conventional reinforcement or water-tightening technology under high-water pressure conditions. In this study, the freezing energy and required time was calculated by the theoretical model of the heat flow to estimate the total amount of refrigerant required for the artificial ground freezing. A lab-scale freezing chamber was devised to investigate changes in the thermal and mechanical properties of sandy soil corresponding to the variation of the salinity and water pressure. The freezing time was measured with different conditions during the chamber freezing tests. Its validity was evaluated by comparing the results between the freezing chamber experiment and the numerical analysis. In particular, the freezing time showed no significant difference between the theoretical model and the numerical analysis. The amount of refrigerant for artificial ground freezing was estimated from the numerical analysis and the freezing efficiency obtained from the chamber test. In addition, the energy ratio for maintaining frozen status was calculated by the proposed formula. It is believed that the energy ratio for freezing will depend on the depth of rock cover in the subsea tunnels and the water temperature on the sea floor.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.2
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• pp.151-163
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• 2006

Although various methods for effective modeling of pre-reinforced zones have been suggested for numerical analysis of large section tunnels, tunnel designers refer to empirical cases and literature reviews rather than engineering methods because ones who use commercial programs are unfamiliar with a macro-scale approach in general. Therefore, this paper suggests a simple micro-scale approach combined with the macro-scale approach to determine equivalent design parameters for effective numerical modeling of pre-reinforced zones in tunnel. This new approach is to determine the equivalent stiffness of pre-reinforced zones with combination of ground, bulb, and steel in series or/and parallel. For verification, 3-D numerical results from the suggested approach are compared with those of a realistic model. The comparison suggests that two cases make best approximation to a realistic solution: One is related to the series-parallel stiffness system (hereafter SPSS) in which bulb and steel are coupled in parallel and then connected to the ground in series, and the other is the series stiffness system (hereafter SSS) in which only bulb and steel are coupled in series. The SPSS is recommended for stiffness calculation of pre-reinforced zones because the SSS is inconvenient and time-consuming. The SPSS provides slightly bigger vertical displacement at tunnel crown in weathered rock than other cases and give almost identical results to a realistic model for horizontal displacement at tunnel spring line and ground surface settlement. Displacement trends on weathered rock and weathered soil are similar. The SPSS which is suggested in this paper represents the behavior mechanism of pre-reinforced area effectively.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.1
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• pp.83-97
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• 2018

Tunnels are widely used for special purposes including roads, railways and culvert for power transmission, etc. Its cross-section shape is determined by uses, ground condition, environmental or economic factor. Many papers with respect to behaviours of adjacent ground and existing structure tunnelling-induced have been published by many researchers, but tunnel cross-section have rarely been considered. A collapse of tunnel causes vaster human and property damage than structures on the ground. Thus, it is very important to understand and analyse the relationship between behavoiurs of ground and cross-section type of tunnel. In this study, the behaviour of ground due to tunnel excavation for underground station below the grouped pile supported existing structure was analysed through laboratory model test using a trap-door device. Not only two cross-section types, 2-arch and box, as station for tunnel, but also, offset between tunnel and grouped pile centre (0.1B, 0.25B, 0.4B) are considered as variable of this study. In order to measure underground deformation tunnelling-induced, Close Range Photogrammetry technique was applied with laboratory model test, and results are compared to numerical analysis.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.1
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• pp.91-105
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• 2020

This study is the basic study for improving the range of influence and potency of mixing bars in the chamber of Shield TBM. Currently, there are many studies on disk cutters, cutter bits and segments in the study of the domestic Shield TBM. However, studies that mix soil and rocks that come from the membrane during the Shield TBM excavation and scatter them with screw conveyors are not as good as those abroad. In this study, the existing Shield TBM Chamber was manufactured as a miniature and the experiment. Inside the chamber, different sizes (4 mm, 6 mm, 8 mm, 10 mm) and colors (black, white, red, and blue) were used to form layers. This experiment was carried out by different shapes and sizes of RPM and mixing bars. In addition, the difference between a miniature model and a reclining one was checked to determine the effect of the direction of gravity on the mixing efficiency. This was done in the same way for all other conditions other than differences in the direction of gravity. Through this experiment, we identified the orientation of the chamber model, the size and shape of the mixing bar inside, and the mixing effect and torque depending on RPM. A comparative review of the mixing effect and torque confirmed that the shape and size of the mixing bar affect the mixing of samples, and that the direction of gravity affects torque.

• Journal of Applied Biological Chemistry
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• v.54 no.4
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• pp.296-302
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• 2011

Insect-resistant transgenic rice was developed by inserting the mCry1Ac1 a modified gene from the soil bacterium Bacillus thuringiensis (Bt). For biosafety assessment, we studied the effects on survival of cantor Daphnia magna, a commonly used as a model organism in ecotoxicological studies. D. magna fed on Bt rice and its near non-genetically modified (GM) counterparts (Nakdong) grown in the same environment (100% ground rice suspension). The Bt rice was comfirmed to have the insertion of T-DNA and protein expression by the polymerase chain reaction and ELISA analysis. Feeding study showed similar cumulative immobility and abnormal response of D. magna between Bt rice and non-GM counterparts. 48 h-$EC_{50}$ values of Bt rice and non-GM rice showed 4,429 and 2,889 mg/L respectively. The rice no observed effect concentration (NOEC) values for D. magna was suggested 1,000 mg/L. We conclude that the tested Bt-rice and Nakdong similar cumulative immobility for D. magna the widely used model organism. We found out that there is strong possibility that the growth of Bt rice didn't affect to non-target insects.

• Journal of Korean Society for Atmospheric Environment
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• v.29 no.1
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• pp.74-85
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• 2013

Since the underground transportation system is a closed environment, indoor air quality problems may seriously affect many passengers' health. The purpose of this study was to understand $PM_{10}$ characteristics in the underground air environment and further to quantitatively estimate $PM_{10}$ source contributions in a Seoul Metropolitan subway station. The $PM_{10}$ was intensively collected on various filters with $PM_{10}$ aerosol samplers to obtain sufficient samples for its chemical analysis. Sampling was carried out in the M station on the Line-4 from April 21 to 28, July 13 to 21, and October 11 to 19 in the year of 2010 and January 11 to 17 in the year of 2011. The aerosol filter samples were then analyzed for metals, water soluble ions, and carbon components. The 29 chemical species (OC1, OC2, OC3, OC4, CC, PC, EC, Ag, Al, Ba, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Si, Ti, V, Zn, $Cl^-$, $NO_3{^-}$, $SO_4{^{2-}}$, $Na^+$, $NH_4{^+}$, $K^+$, $Mg^{2+}$, $Ca^{2+}$) were analyzed by using ICP-AES, IC, and TOR after proper pretreatments of each sample filter. Based on the chemical information, positive matrix factorization (PMF) model was applied to identify the $PM_{10}$ sources and then six sources such as biomass burning, outdoor, vehicle, soil and road dust, secondary aerosol, ferrous, and brakewear related source were classified. The contributions rate of their sources in tunnel are 4.0%, 5.8%, 1.6%, 17.9%, 13.8% and 56.9% in order.

• Journal of the Korean Society for Marine Environment & Energy
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• v.4 no.4
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• pp.3-11
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• 2001

To know the seawater infiltration into tidal flat sediment in coastal area is very important, because it is significantly correlated with the infiltration and transportation of pollutants in soil, the supply of dissolved oxygen, nutrients and organic matter to benthic organisms for survival of benthic organisms and the seawater purification. So, we set up purpose to clarify the infiltration behavior of seawater by wave action in tidal flat, to clear the effects of slope of tidal flat and breaking wave height on seawater infiltration and to quantify the infiltration volume of seawater. For purpose, the seawater infiltration was studied with visualization method by using coloring tracer and transparent glass beads replaced as natural sediment in model tidal flat. Specific conclusions derived from this study are as follows. The semi-circular type infiltration of seawater by wave action into saturated sediment was a new infiltration behavior that was not considered in previous studies. The infiltration rate of seawater was increased with increasing of breaking wave height and slope of tidal flat. However, the effects of the slope was bigger than that of breaking wave height on seawater infiltration into tidal flat sediments. It was possible to calculate the infiltration volume of seawater by wave action in natural tidal flat sediment and in fields. Therefore, we can point out that wave action play an important role in the supply of dissolved oxygen, nutrients and organic matter to benthic organisms, transportation or diffusion of pollutants and seawater purification. So, we hope to be studied the supply of food to benthic organism, pollutant transport and seawater purification on the base of these results.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1077-1081
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• 2008

Soil and Water Assessment Tool(SWAT) 모형은 DEM(Digital Elevation Model)을 사용하여 지형인자를 추출하고 이를 바탕으로 수문 및 수질 모의가 이루어진다. 지형인자의 추출시 DEM 격자크기에 따라 상이한 결과를 초래할 수 있다. 그리하여 정확한 수문 및 수질 모델링에 있어 가능한 고해상도의 DEM을 사용하도록 권장하고 있다. 그러나 넓은 유역에서의 적용시 고해상도 DEM 사용에 따른 컴퓨터 처리 용량과 프로그램 실행 시 소요되는 시간상의 문제는 그 효율성에 있어서 문제시될 수 있다. 그리하여 본 연구에서는 소양강댐, 임하댐 유역을 대상으로 SWAT 모형에서 저해상도 DEM 사용으로 고해상도 DEM의 지형인자를 추출하여 자동 입력될 수 있는 모듈을 개발 적용하였다. 본 연구의 결과 소양강댐 유역을 대상으로 격자크기 20m DEM과 100m DEM을 사용하였을 때 연평균 유사량이 83.8%의 큰 차이가 발생한 반면 격자크기의 20m DEM과 본 모듈을 적용하여 20m DEM의 지형인자로 자동 보정된 100m DEM을 사용하였을 때의 연평균 유사량이 4.4%로 차이가 상당히 줄어든 것을 볼 수 있었다. 임하댐 유역의 경우는 격자크기 10m DEM과 100m DEM을 사용하였을 때 연평균 유사량이 43.4% 큰 차이가 발생하였다. 반면 격자크기 10m DEM과 본 모듈을 적용하여 10m DEM의 지형인자로 자동 보정된 100m DEM을 사용하였을 때의 연평균 유사량이 0.3%로 차이가 크게 줄어든 것을 확인 할 수 있었다. 또한 본 모듈의 검정을 위해 소양강댐 유역의 지형 자료와 유사한 충주댐 유역을 대상으로 본 모듈을 적용하여 검정을 실시하였다. 그 결과 연간 평균 유사량이 격자크기 20m와 100m의 DEM을 이용하였을 때 98.7%의 큰 차이가 발생한 반면 격자크기 20m와 본 모듈을 적용하여 보정된 경사도 값의 100m DEM을 사용하였을 때 20.7%로 차이가 크게 줄어든 것을 볼 수 있었다. 그리하여 본 연구의 결과를 통해 SWAT 모형에서의 개선된 지형인자 추출 방식을 사용하여 저해상도의 DEM 사용으로 고해상도 DEM 사용의 효과를 볼 수 있을 것이고 이로 인해 넓은 유역에서 저해상도 DEM 사용으로 컴퓨터 사용용량과 프로그램 지연 시간을 줄일 수 있을 것으로 판단된다. 향후 여러 유역을 대상으로 보정, 검정하여 보다 정확하고 통합적으로 적용될 수 있는 모듈의 개선이 필요할 것으로 사료된다.

• Journal of Korea Water Resources Association
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• v.49 no.11
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• pp.931-939
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• 2016

Bangudae Petroglopys of the national treasure No. 285 located in elevation of 53 m to 57 m have been damaged by repetition of submergence and exposure due to the Sayeon-dam of EL.60 m constructed in down stream. In this study, as a preservation plan of the petroglyphs from the contact with water, the construction of eco-levee was suggested and its effect was investigated in the views of hydraulic engineering. It was designed to be located aside of 80 m from Bangudae Petroglyphs with the length of 440 m in streamwise direction, and it was need to construct a new channel maintaining the original hydraulic capacity and conveyance. Hydraulic characteristics such as water surface elevations and velocities near Bangudae Petroglyphs were measured after the eco-levee was installed in the hydraulic model with the scale of 1:50. It showed that there were not much changes of water surface elevations and velocities between sayeon-dam spillway EL. 60 m (Suggestion 1) and EL. 54 m (Suggestion 2). It was concluded the eco-levee could be made of natural materials like soil, pebble, gravel in terms of allowable velocity and shear stresses. The slope of water surface at Suggestion 2 was steeper, and velocities near Bangudae Petroglyphs were also faster than Suggestion 1. As the vorties occured at the left side in Suggestion 2, more detailed study is required.

• Journal of Korea Water Resources Association
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• v.50 no.6
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• pp.373-386
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• 2017

This study simulated water quality item and flow rate of subbasin for Saemangeum watershed using Soil and Water Assessment Tool (SWAT) model and Environmental Fluid Dynamics Code (EFDC) model which simulate hydraulic and water quality in three-dimensions. The simulated values corresponded to observed value well. The result of simulation for floodgate operations at the M3 and M5 points, it exceeds water quality standard and at the M3 and D3 points, change of range for concentration is too wide, and upstream of Saemangeum reservoir is sensitive to inflow flow rate. Compared to the annual average concentration for observed station according to the discharge conditions, improvement of water quality for upstream was apparently compared to the downstream. Range of influence for change of water quality presented that maximum discharge condition, the influence range is 22 km in the direction of the Saemangeum downstream from the Mankyung bridge, and 15 km in the downstream direction of saemangeum in the Dongjin bridge. This study result demonstrated that floodgate operating at upstream has significant influence on water quality management of Saemangeum reservoir and it needs to be considered in plans of water quality management for Floodgate operation on Saemangeum reservoir.